The cornerstone of aeronautics, avionics, and spacecraft design has been the ability to design lightweight components that maintain structural strength and integrity. These characteristics play a crucial role not only in traditional design considerations such as flight capabilities and structural integrity, but also play a crucial role in the adaptability and commercial performance of a given craft design. Reduced weight and structural fortitude can play a significant role in fuel consumption, craft profile, and cargo and/or passenger capacity. The increase in profitability associated with the aforementioned factors, as well as a variety of others, has provided strong motivation for design advancements in the area of strength/weight improvement.
A significant advancement in the development of low weight/high strength structures was the development of the hollow cell cores, such as honeycomb cores. Hollow cell cores provide a high strength structural base while minimizing the negative effects of the weight associated with the core material by containing voids within the core material that provide for significant weight savings as compared to a solid component. The high strength/low weight characteristic of hollow cell cores has therefore resulted in the popularity of their use within the aeronautics industry as well as a variety of other industries.
Despite the popularity of hollow cell core materials, such as honeycomb cores, there use has not been suitable for certain manufacturing processes. Liquid molding processes, for example, can present problems when applied to hollow cell core materials. Liquid molding composite manufacturing processes, such as resin transfer molding, vacuum assisted resin infusion, vacuum infusion molding, and others, present fundamental concerns for the use of hollow cell core materials. When these processes are used, it is possible for the hollow cells to fill with liquid resin prior to curing. This can make the resulting structure resin rich, heavy, and generally undesirable. It would be highly desirable to have the ability to apply liquid molding approaches to hollow cell core materials without the concerns for compromised cells.
Numerous approaches have been developed in an attempt to solve the hollow cell core/liquid molding dilemma. Often, however, the resulting solutions add undesirable weight and/or production costs to the resulting hollow core composite articles. One solution pre-processes the core to seal the cells with film adhesive, or film adhesive and prepreg, prior to liquid molding composite article fabrication to prevent liquid molding resin from penetrating the cells. Other processes include filling the hollow cells, for example, with a closed cell foam or material. This, however, often adds undesirable weight to the resulting article. Procured composite sheets autoclaved to the hollow cell core add additional weight and require a costly autoclaving process. Although a variety of other attempts are known to seal the hollow cell core, often these attempts result in undesirable weight increases, increases in the number of processing steps, and undesirable cost increases.
It would, therefore, be highly desirable to have a method for sealing hollow cell core material such that the hollow cell core material may be successfully used with known liquid molding approaches without penetration of the hollow cells by the liquid molding. In addition, it would be highly desirable for such a protective hollow cell core material to withstand liquid molding approaches without undesirable increases in weight or the requirement for costly manufacturing processes.